Petroleum coke (petcoke) is a carbonaceous solid derived from oil refinery coker units or other cracking processes. It is a by-product from oil refineries and is mainly composed of carbon. Fuel grade petcoke also contains high levels of sulphur. There has been considerable interest in petcoke for many years, as it is normally cheaper than coal and has a very high calorific value. There are three types of petcoke, which are been produced depending on the process of production. There exist delayed, fluid and flexi coking with delayed coking constituting over 90% of the total production. All three types of petcoke have higher calorific values than coal and contain less volatile matter and ash.
The main uses of petcoke are as energy source for cement production, power generation and iron and steel production. There are many constraints for effective utilization of petcoke as a fuel in cement industry. One of these constraints is the hardness of petcoke, its hardness is greater than coal and hence the power consumption of the grinding systems is increased. Due to its low content of volatile matter, petcoke has poor ignition and burnout characteristics. Therefore, petcoke has to be ground to a much higher fineness than conventional fuels in order to allow its use as fuel in cement kilns or calciners. However, petcoke is difficult to grind, primarily because of its high carbon content that has a lubricating effect, so that petcoke shows a lesser tendency towards comminution by attrition and abrasion in the grinding systems.
A further problem associated with the firing of petcoke in cement kilns or calciners is its high sulphur content. Due to the high levels of excess air required for petcoke combustion the SO2 emissions are relatively high. In the course of the clinkering process SO2 is absorbed into the cement clinker as sulphates. Due to the high sulphur content operational issues also can arise during petcoke firing in cement kilns, such as blockage at kiln inlets and in preheater and precalciner cyclones.
U.S. Pat. No. 4,162,044 discloses a process for grinding of coal or ores in a liquid medium with use of a grinding aid comprising an anionic polyelectrolyte derived from polyacrylic acid in order to increase the grinding efficiency.
U.S. Pat. No. 4,136,830 discloses a process for grinding coal or ores containing metal values comprising carrying out said grinding in a liquid medium and with a grinding aid comprising copolymers or salts of copolymers of styrene with maleic anhydride, in order to increase the grinding efficiency.